1. Field of the Invention
The present invention relates to a wheel speed correction device, and more particularly, to a wheel speed correction device which appropriately corrects each wheel speed with respect to the changes in the diameter of the corresponding tire and the changes in wheel speed which occur when the vehicle turns, and thereby accurately calculates the wheel speed of each wheel.
2. Description of the Prior Art
For a wheel behavior control, such as an antilock brake control or a traction control, it is necessary to obtain the circumferential wheel speed. However, because it is difficult to directly measure the circumferential wheel speed, the wheel rotation angular speed is generally measured and converted to the circumferential wheel speed using appropriate coefficient representing the tire diameter. The term "wheel speed" generally used herein means circumferential wheel speed. The wheel speed thus obtained is known, however, to become offset from the real vehicle speed for a variety of reasons. Causes for the difference between the wheel speed and vehicle speed, i.e., the deviation, include: (i) in the long-term, differences in the real tire diameter and the tire diameter used in the calculation; (ii) in the mid-term, differences in the paths of the left and right wheels followed when the vehicle turns; and (iii) in the short-term, abnormal slipping between the tire and road surface. Variations in the tire diameter may arise due to differences in operating conditions, such as the tire air pressure and/or amount of tire wear.
However, in conventional control systems, specifically in wheel behavior control such as the antilock brake control which should be applied only to the variations caused by factor (iii) above, control is usually applied based on the wheel speed which includes deviations caused by the tire diameter and deviations caused by turning of the vehicle. Thus, when these deviations have become so great that they cannot be ignored, special logic which accounts for abnormal tire diameter becomes necessary to handle the deviations caused by factor (i), and special logic which accounts for vehicle turning becomes necessary to handle the deviations caused by factor (ii), and the wheel behavior control logic therefore tends to become complex.